It is known to continuously dye textile fibrous materials, such as loose staple fibers, by impregnating the fibers with a liquid dye or other chemical, and thereafter continuously passing the fibers through a confined high frequency energy heating zone to react and fix the dye or other chemical on the fibers. As used herein, the terms "liquid dye or other chemical" means any dye or other chemical which is in a liquid medium form when applied to the textile fibrous materials.
U.S. Pat. No. 4,104,019 discloses process and apparatus for the fixation of dyes or other chemicals onto textile fibers by continuously passing the same through a confined radio frequency energy heating tube. The fibers are compressed and compacted in the confined heating tube to form a partially self-sealing pressure chamber whereby generation of steam from the wetted fibers accelerates the reaction of the dye on the fibers. A copending commonly assigned Beucus U.S. patent application Ser. No. 390,207 discloses method and apparatus for continuously dyeing textile fibrous materials using radio frequency energy to react the dye on the fibers, as referred to in U.S. Pat. No. 4,104,019. Said copending application relates to an improvement wherein the loose fibrous materials may be dyed at a greater rate of production by intermittent batch-wise delivery to a compression chamber and ram assembly which introduces the dye-wetted fibers under compression into the confined heating tube.
In such continuous treatment of textile fibrous materials by compressed passage through a confined radio-frequency energy heating tube, it has been found that loose masses of certain synthetic staple fibers having thermoplastic properties, in particular acrylic fibers, are quite bulky and have such a high loft and volume that they are difficult to effectively compact and compress at a high rate of production. In particular, even with the intermittent delivery of acrylic fibers into a compression chamber as described in the aforesaid copending U.S. patent application, the apparatus can effectively handle only up to about 500 pounds of dry weight acrylic fiber per hour. For greater economy of production, it is of course desirable to further increase the capacity of the apparatus for handling and dyeing or otherwise chemically treating textile fibrous materials.
It has also been found that in the continuous high speed dyeing of loose textile fibers, in particular, synthetic fibers utilizing the high frequency heating apparatus described in U.S. Pat. No. 4,104,019, problems can also occur in obtaining uniform distribution and fixation of the dye color in the compressed fibrous mass. Such is believed due to non-uniform packing of the fibrous mass in the confined heating tube which produces density variations in the mass. In particular, if the packing density varies across or along the length of the mass of fibers in the tube, the concentration of the liquid phase which constitutes the lossy material in the heating tube will also vary, causing corresponding temperature variations in the mass being heated by radio frequency energy. Such temperature variations accordingly produce differential dye reactivity and color shade variations in the fibers.